Reflecting sheets are used as reflectors for reflecting light of a point-like or linear light source, such as LEDs and cold-cathode tubes, in plane form to thereby obtain a uniform plane-like light source in liquid crystal display devices, and particularly, used as reflectors of direct backlights of large-size liquid crystal display devices of liquid crystal televisions and the like. Conventionally, as the reflecting sheet, used are sheets containing fine voids inside thereof and sheets with a metal reflecting layer of silver or the like provided on their surface.
In the large-size liquid crystal display device of the large-size liquid crystal television or the like, a plurality of cold-cathode tubes that are linear light sources is arranged in parallel and used to lighten the display screen. In this case, streak-shaped lamp images derived from the cold-cathode tubes tend to occur, and therefore, by using a reflecting sheet that causes diffuse reflection among the reflecting sheets, it is intended to reduce the lamp images.
As the reflecting sheet that causes diffuse reflection, sheets containing fine voids inside thereof are generally used, and for example, include reflecting sheets obtained by stretching a sheet such that inorganic powder is added to a polyester resin or polypropylene resin and thereby forming fine voids originating from the inorganic powder, and sheets obtained by impregnating a sheet made of a polyester resin with a nitrogen gas or carbon dioxide gas to foam.
The light which is emitted from linear light sources such as cold-cathode tubes and reflected by these reflecting sheets tends to cause streak-shaped fluctuations in the level of brightness i.e. lamp images. This is because areas immediately above the cold-cathode tubes are bright while areas between the cold-cathode tubes are dark. In the large-size liquid crystal television and the like, to evenly reflect the incident light, it is generally performed that a diffuser is used before the reflected light enters the liquid crystal panel to uniformize the luminance of the light entering the liquid crystal panel. At this point, by setting a long distance (>20 mm) between the reflecting sheet and the diffuser, a distance is put in between the cold-cathode tubes and the reflecting sheet, and the lamp images are reduced. Further, by installing various optical sheets above the diffuser, it is intended to reduce lamp images.
However, at present, with attention directed toward further super-slim TVs, it is strongly desired to make the direct type ultra-thin. As the backlight is ultra-thinned, there is a tendency that the lamp images derived from the cold-cathode tubes increases, and reductions in the lamp image are a significant issue in super-slim TV development.
Meanwhile, in parallel with the super-slimming, at present, with attention directed toward reductions in the cost and increases in energy saving in the liquid crystal TV, it is strongly desired to decrease the cold-cathode tubes of the direct type backlight i.e. save the lamp. As the cold-cathode tubes of the backlight are decreased, the spacing between the cold-cathode tubes increases, the lamp images derived from the cold-cathode tubes tend to increase, and reductions in the lamp image are a significant issue in saving the lamp.    [Patent Document 1] Japanese Examined Patent Publication No. H06-89160    [Patent Document 2] Japanese Patent Gazette No. 2925745